It is well known to utilize embossing to decorate and thicken tissue products. An abundance of prior art exists which demonstrates these utilities, including U.S. Pat. No. 2,043,351 to Fourness, U.S. Pat. No. 4,189,344 to Busker, and U.S. Pat. No. 5,356,364 to Veith. Using embossing to increase sheet caliper (thicken), has allowed bathroom tissue producers to reduce the number of sheets within the roll while retaining the same package size (roll diameter). This has been a common practice in the bathroom tissue market over the past 20-25 years, particularly for household tissue products sold at grocery stores. It has not been prevalent in the service and industrial market, where it is more desireable to have high sheet counts so that the rolls last longer and have to be replenished less frequently. Also, these products are typically not so lavishly decorated with embossing as are the household tissue products.
One very popular form of decorative bathroom tissue embossing has come to be known in the trade as "spot embossing", referenced in U.S. Pat. No. 4,659,608 to Schultz. Spot embossing generally involves discrete embossing elements that are about 1/2 inch by 1/2 inch to about 1 inch by 1 inch in size (about 0.25 to about 1 square inch in surface area). These discrete spot embossing elements are spaced about 1/2 inch to about 1 inch apart. They are typically engraved in a steel roll about 0.060 inch in relief. In most cases spot embossing is carried out with a steel engraved roll (male elements) and a rubber covered backing roll. The design of spot embossing patterns covers a wide range of decorative shapes, some of which are the subject of design patents. For example, Kimberly-Clark has a butterfly design (U.S. Pat. No. D305,182). Other spot designs used commercially include American Can's flower (D260,193), Georgia-Pacific's angels (D332,874), Georgia-Pacific's swans (D332,875), and Potlatch's flower (D353,053). Spot embossing is commonly used not only to decorate, but also to increase sheet caliper.
In the past several years, some household bathroom tissue producers in the U.S. have begun to increase the sheet counts within the roll in order to give consumers added value. Examples are CHARMIN.RTM. Big Squeeze (450 sheet count) and NORTHERN.RTM. Big Roll (420 sheet count). In May, 1992, Kimberly-Clark went even further and introduced a new product sold under the brand name of KLEENEX.RTM. Premium Bathroom Tissue--Double Roll. This product features winding the length of (2) 280 sheet count rolls into a single roll having 560 sheets. Winding two rolls into one necessarily increases the roll diameter.
However, the roll diameter of bathroom tissue products can not be too large or the rolls will not fit into the dispensers used in most households. Typically the roll diameter needs to be no greater than 5 inches in order to meet this requirement. As one would expect, it has been found to be difficult to emboss bathroom tissue for rolls having high sheet counts, e.g. 500 sheets or more, with the roll diameter constrained to 5 inches or less. This is especially true if the tissue is soft and thick. It has been found that when 500 or more sheets of soft, thick tissue are embossed and wound into a roll 5 inches or less in diameter, the embossing pattern washes out and all but disappears with time because of the high degree of winding tension necessary to attain the target roll diameter.
Therefore there is a need for a method of embossing soft, thick tissue sheets which provides a lasting embossing pattern in tissue sheets wound into high sheet count rolls.